Superconductors of many types are known in the prior art, including both elemental metals and compounds of various types, such as oxides. The recent technical break-through reported by Bednorz and Mueller in Z. Phys. B, 64, 189 (1986) was the first major improvement in a superconducting material in the last decade, wherein the critical transition temperature T.sub.c at which the material becomes superconducting was increased substantially.
Bednorz and Mueller described copper oxide material including a rare earth element, or rare earth-like element, where the rare earth element could be substituted for by an alkaline earth element such as Ca, Ba or Sr.
The work of Bednorz and Mueller has led to intensive investigation in many laboratories in order to develop materials having still higher T.sub.c. For the most part, these high T.sub.c oxide superconductors consist of compounds of La, Sr, Cu and O, or Y, Ba, Cu and O. In particular, copending application Ser. No. 024,653, filed Mar. 11, 1987 and assigned to the present assignee, describes a high T.sub.c oxide superconductor that is a single phase bulk superconductor having the general formula EQU A.sub.1.+-.x M.sub.2.+-.x Cu.sub.3 O.sub.y
where A is Y or a combination of Y, La, Lu, Sc or Yb; M is Ba, or a combination of Ba, Sr or Ca; x is between 0 and 0.5 and y is sufficient to satisfy the valence demands of the material. A particularly preferred single phase composition described in that copending application is Y Ba.sub.2 C.sub.3 O.sub.y.
For many applications, it is necessary to be able to provide the superconducting material in film form, i.e., in a range of thin films (for example, about 1000 angstroms) to thick films (for example, in excess of 1 micron). Heretofore, there has been no reported satisfactory way to provide films of these new high T.sub.c oxide superconductors where the films must exhibit superconductivity at temperatures in excess of 40.degree. K. Accordingly, it is a primary object of the present invention to provide films of high T.sub.c oxide superconductors having superconductivity at temperatures in excess of 40.degree. K, and methods for preparing these films.
It is another object of this invention to provide copper oxide superconducting films exhibiting superconductivity at temperatures in excess of 40.degree. K, and methods for preparing these copper oxide high T.sub.c films.
It is another object of the present invention to provide transition metal oxide superconductive films having superconductivity at temperatures in excess of 40.degree. K, and methods for preparing these transition metal superconducting oxides.
It is another object of the present invention to provide films of transition metal oxide superconductors exhibiting superconductivity at temperatures in excess of 40.degree. K, where the films are continuous and smooth, and exhibit compositional uniformity over useable areas.
It is another object of the present invention to provide continuous, smooth copper oxide superconductive films exhibiting superconductivity at temperatures in excess of 40.degree. K and methods for making these films, where the films exhibit perovskite-like structure.
It is another object of this invention to provide transition metal oxide superconductive films including a rare earth element, or rare earth-like element, where the films exhibit superconductivity at temperatures greater than 40.degree. K, and methods for making these films.
It is another object of the present invention to provide films having the nominal composition .LAMBDA.BO.sub.3-y or .LAMBDA.BO.sub.y exhibiting superconductivity at temperatures greater than 40.degree. K, where .LAMBDA. stands for a rare earth or near rare-earth element or a combination of a rare earth element and an element selected from the group consisting of Ca, Ba and Sr, B stands for a transition metal, and y is sufficient to satisfy the valence demands of the film composition.
It is another object of this invention to provide superconductive oxide films having the nominal composition AB.sub.2 Cu.sub.3 O.sub.9-y, and methods for making these films, where the films are superconducting at temperatures in excess of 40.degree. K and A is a rare earth or rare earth-like element, B is an alkaline earth element, and y is sufficient to satisfy valence demands of the composition.
It is another object of the present invention to provide smooth, continuous copper oxide superconducting films having a perovskite-like crystal structure and exhibiting superconductivity at temperatures in excess of 40.degree. K, and to provide methods for making these films.